1. Field of the Invention
The invention relates to a sleeve bearing arrangement using a new material, and more particularly, the invention provides a maintenance-free sleeve bearing that does not require resupply of oil during operation. At the same time, it is an object of the invention to provide a sleeve bearing using a high-tech eco-material (state-of-the-art material excellent in ecological adaptability) obtained from biomass type resources, different from conventional industrial material.
2. Description of the Related Art
In the past, sleeve bearings made of a resin such as a polyacetal, a polyamide, etc. have been in use for rotating parts which are light in weight and slow in rotational speed because such sleeve bearings are available at a low cost in comparison with sleeve bearings made of metal.
However, as a lubricating oil is required between a shaft and a sleeve bearing, a method of lengthening the service life of the sleeve bearing has been under study. There are available various methods such as a method of increasing an amount of oil by increasing a volume of a shaft impregnated with oil, a method of replenishing oil by providing an oil pan, a method of preventing spilling of oil by devising an oil seal, and so forth. However, any of these methods has both merits and demerits, and there is room left for improvement.
The inventor of the present invention has conducted intense studies, and found out that a porous material is obtained by a process comprising the steps of mixing degreased bran derived from rice bran with a thermosetting resin before kneading, subjecting a kneaded mixture to a primary firing in an inert gas at a temperature in a range of 700 to 1000xc2x0 C., pulverizing the kneaded mixture obtained after the primary firing into carbonized powders sieved through 100 mesh, mixing the carbonized powders with a thermosetting resin before kneading, pressure-forming a kneaded mixture thus obtained at a pressure in a range of 20 to 30 MPa, and applying a heat treatment again to a formed kneaded mixture in the inert gas at a temperature in a range of 100 to 1100xc2x0 C., and the porous material thus obtained (referred to hereinafter as CRB ceramics) has ideal characteristics as material suitable for use in sleeve bearings.
Further, it has been found that the CRB ceramics described above are insusceptible to damage, light in weight, and have a long service life, and have in addition the ability to retain oil and grease for a long period of time. It has also been found that the porous material not only has ideal characteristics as a material suitable for use in the sleeve bearings but also has a small contraction ratio of the dimensions of a workpiece formed thereof to those of a finished product.
More specifically, the porous material described above has the contraction ratio of the dimensions of a workpiece formed thereof to those of the finished product, as small as 3% or less, 13 wt % of oil retention characteristic, 4.85xc3x9710xe2x88x923 xcexa9cm of volume resistivity, and a density in a range of 1.05 to 1.3 g/cm3, and further, it has been possible to obtain the porous material having suitable hardness, and still have a friction coefficient in the order of about 0.15 after being fired at a high temperature.
The inventor of the present invention has found out that it is possible to fabricate a sleeve bearing arrangement, having diverse characteristics, by forming a sleeve bearing from the porous material (the CRB ceramics) obtained by the process comprising the steps of mixing degreased bran derived from rice bran with a thermosetting resin before kneading, subjecting a kneaded mixture to a primary firing in an inert gas at a temperature in a range of 700 to 1000xc2x0 C., pulverizing the kneaded mixture obtained after the primary firing into carbonized powders sieved through a screen of 100-mesh, mixing the carbonized powders with a thermosetting resin before kneading, pressure-forming a kneaded mixture thus obtained at a pressure in a range of 20 to 30 MPa, and applying a heat treatment again to a formed kneaded mixture in the inert gas at a temperature in a range of 100 to 1100xc2x0 C., or by combining a conventional sleeve bearing formed of a synthetic resin or a steel-based metal with a shaft formed of the CRB ceramics. First, a typical sleeve bearing arrangement is shown in FIG. 1 wherein reference numeral 1 denotes a shaft, and reference numeral 2 denotes a sleeve bearing.
With the present invention, the shaft 1, and/or the sleeve bearing 2 are formed of the CRB ceramics.